Degradation kinetics and formation of regulated and emerging disinfection by-products during chlorination of two expectorants ambroxol and bromhexine.

Ambroxol hydrochloride (AMB) and bromhexine hydrochloride (BRO) are classic expectorants and bronchosecretolytic pharmaceuticals. In 2022, both AMB and BRO were recommended by medical emergency department of China to alleviate cough and expectoration for symptoms caused by COVID-19. The reaction characteristics and mechanism of AMB/BRO with chlorine disinfectant in the disinfection process were investigated in this study. The reaction of chlorine with AMB/BRO were well described by a second-order kinetics model, first-order in both AMB/BRO and chlorine. The second order rate reaction constant of AMB and BRO with chlorine at pH 7.0 were 1.15 × 102 M-1s-1 and 2.03 × 102 M-1s-1, respectively. During chlorination, a new class of aromatic nitrogenous disinfection by-products (DBPs) including 2-chloro-4, 6-dibromoaniline and 2, 4, 6-tribromoaniline were identified as the intermediate aromatic DBPs by gas chromatography-mass spectrometry. The effect of chlorine dosage, pH, and contact time on the formation of 2-chloro-4, 6-dibromoaniline and 2, 4, 6-tribromoaniline were evaluated. In addition, it was found that bromine in AMB/BRO were vital bromine source to greatly promote the formation of classic brominated DBPs, with the highest Br-THMs yields of 23.8% and 37.8%, respectively. This study inspired that bromine in brominated organic compounds may be an important bromine source of brominated DBPs.

Transformation of antiviral ribavirin during ozone/PMS intensified disinfection amid COVID-19 pandemic.

Due to the spread of coronavirus disease 2019 (COVID-19), large amounts of antivirals were consumed and released into wastewater, posing risks to the ecosystem and human health. Ozonation is commonly utilized as pre-oxidation process to enhance the disinfection of hospital wastewater during COVID-19 spread. In this study, the transformation of ribavirin, antiviral for COVID-19, during ozone/PMS­chlorine intensified disinfection process was investigated. •OH followed by O3 accounted for the dominant ribavirin degradation in most conditions due to higher reaction rate constant between ribavirin and •OH vs. SO4•- (1.9 × 109 vs. 7.9 × 107 M-1 s-1, respectively). During the O3/PMS process, ribavirin was dehydrogenated at the hydroxyl groups first, then lost the amide or the methanol group. Chloride at low concentrations (e.g., 0.5- 2 mg/L) slightly accelerated ribavirin degradation, while bromide, iodide, bicarbonate, and dissolved organic matter all reduced the degradation efficiency. In the presence of bromide, O3/PMS process resulted in the formation of organic brominated oxidation by-products (OBPs), the concentration of which increased with increasing bromide dosage. However, the formation of halogenated OBPs was negligible when chloride or iodide existed. Compared to the O3/H2O2 process, the concentration of brominated OBPs was significantly higher after ozonation or the O3/PMS process. This study suggests that the potential risks of the organic brominated OBPs should be taken into consideration when ozonation and ozone-based processes are used to enhance disinfection in the presence of bromide amid COVID-19 pandemic.

The occurrence and control of waterborne viruses in drinking water treatment: A review.

As the coronavirus disease 2019 continues to spread globally, its culprit, the severe acute respiratory syndrome coronavirus 2 has been brought under scrutiny. In addition to inhalation transmission, the possible fecal-oral viral transmission via water/wastewater has also been brought under the spotlight, necessitating a timely global review on the current knowledge about waterborne viruses in drinking water treatment system - the very barrier that intercepts waterborne pathogens to terminal water users. In this article we reviewed the occurrence, concentration methods, and control strategies, also, treatment performance on waterborne viruses during drinking water treatment were summarized. Additionally, we emphasized the potential of applying the quantitative microbial risk assessment to guide drinking water treatment to mitigate the viral exposure risks, especially when the unregulated novel viral pathogens are of concern. This review paves road for better control of viruses at drinking water treatment plants to protect public health.

Ecotoxicological effects of disinfected wastewater effluents: a short review of in vivo toxicity bioassays on aquatic organisms. (Themed issue on drinking water oxidation and disinfection processes.)

Wastewater disinfection has attracted attention with regard to fecal-oral transmission during the current coronavirus disease 2019 (COVID-19) outbreak in China. Disinfection reduces the risk posed by waterborne pathogens;however, it threatens ecological safety. Comprising residual disinfectants, disinfection byproducts (DBPs), and other contaminants, disinfected wastewater effluents have a negative impact on aquatic organisms as well as on the balance of the aquatic ecosystem of the recipient water body. Here, we reviewed the in vivo toxicity bioassays of disinfected wastewater effluents on the aquatic organisms at different trophic levels, including freshwater organisms and marine organisms. Associated variables, i.e., total suspended solids (TSSs), ammonia nitrogen (NH3-N), residual disinfectants, and features of the effluent (water temperature and sampling season), can significantly influence the results of these in vivo toxicity bioassays. Each typical test organism has its own pros and cons, where the species type, life stages, and test endpoints have crucial influences on the bioassays;therefore, they should be taken into account before and during the studies on ecotoxicological effects. More efforts should be expended toward conducting more practical bioassays involving the scenarios of the recipient water body in order to better simulate real ecotoxicological effects of disinfected wastewater effluents;extended exposure time should be considered to gain additional insights into the long-term or pass-generation ecotoxicological effects, approaching true levels in the recipient water body.

Effect of oxidation ditch and anaerobic-anoxic-oxic processes on CX3R-type disinfection by-product formation during wastewater treatment.

The high chlorine dosages in wastewater treatment plants during the COVID-19 pandemic may result in increased formation of disinfection by-products (DBPs), posing great threat to the aquatic ecosystem of the receiving water body and the public health in the downstream area. However, limited information is available on the effect of biological wastewater treatment processes on the formation of CX3R-type DBPs. This study investigated the effect of oxidation ditch (OD) and anaerobic-anoxic-oxic (AAO), two widely used biological wastewater treatment processes, on the formation of five classes of CX3R-type DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetaldehydes (HALs), haloacetonitriles (HANs) and halonitromethanes (HNMs), during chlorination. Experimental results showed that biological treatment effectively reduced the dissolved organic carbon (DOC) and UV254, while it increased the dissolved organic nitrogen (DON), and therefore the ratio of DON/DOC. In addition, increases in the contents of soluble microbial product- and humic acid-like matters, and the transformation of high molecular weight (MW) fractions in the dissolved organic matter into low MW fractions were observed after OD and AAO processes. Although biological treatment effectively decreased the formation of Cl-THMs, Cl-HAAs, Cl-HANs and Cl-HNMs, the formation of DBCM, DBAA, BDCAA, DBCAA, DCAL, TCAL and DBAN (where C = chloro, B = bromo, D = di, T = tri) all increased significantly, due to the increased formation reactivity. Moreover, biological treatment increased the ratio of bromide/DOC and bromine incorporation into THMs, HAAs and DHANs except for HALs and THANs. Different from previous studies, this study revealed that biological treatment increased the formation of some DBPs, especially brominated DBPs, despite the efficient removal of organic matters. It provides insights into the DBP risk control in wastewater treatment, particularly during the COVID-19 pandemic.

Ecotoxicological effects of disinfected wastewater effluents: a short review of in vivo toxicity bioassays on aquatic organisms

Wastewater disinfection has attracted attention with regard to fecal-oral transmission during the current coronavirus disease 2019 (COVID-19) outbreak in China. Disinfection reduces the risk posed by waterborne pathogens;however, it threatens ecological safety. Comprising residual disinfectants, disinfection byproducts (DBPs), and other contaminants, disinfected wastewater effluents have a negative impact on aquatic organisms as well as on the balance of the aquatic ecosystem of the recipient water body. Here, we reviewed the in vivo toxicity bioassays of disinfected wastewater effluents on the aquatic organisms at different trophic levels, including freshwater organisms and marine organisms. Associated variables, i.e., total suspended solids (TSSs), ammonia nitrogen (NH3-N), residual disinfectants, and features of the effluent (water temperature and sampling season), can significantly influence the results of these in vivo toxicity bioassays. Each typical test organism has its own pros and cons, where the species type, life stages, and test endpoints have crucial influences on the bioassays;therefore, they should be taken into account before and during the studies on ecotoxicological effects. More efforts should be expended toward conducting more practical bioassays involving the scenarios of the recipient water body in order to better simulate real ecotoxicological effects of disinfected wastewater effluents;extended exposure time should be considered to gain additional insights into the long-term or pass-generation ecotoxicological effects, approaching true levels in the recipient water body.